U.S. patent number 3,925,762 [Application Number 05/409,738] was granted by the patent office on 1975-12-09 for patient monitoring and data processing system.
This patent grant is currently assigned to General Electric Company. Invention is credited to Thomas W. Anderson, John P. Bahr, Louis J. Heitlinger, John H. Smith.
United States Patent |
3,925,762 |
Heitlinger , et al. |
December 9, 1975 |
Patient monitoring and data processing system
Abstract
A physiological monitoring system for use with patients who are
critically ill utilizes a system structure which is inherently
modular, easily expandable, computer compatible, and "fail soft".
The system is composed of bedside units, central station units and
a central processing unit. Patient information such as dynamic
waveforms, derived physiological parameters, physiological alarms,
trend graphs and multi-parameter plots are provided in addition to
such system information as alarm limits and system alarms. The
system structure is based upon use of digital data buses which
interconnect the units located at the bedside, central station and
central processor. The digital data buses provide two-way
communication between the system units and yet have a relatively
small number of conductors for the amount of information exchanged
between the units. The digital data buses are operated in a
synchronous mode wherein data words appear on the buses in a
predetermined time relationship relative to repetitive
synchronizing pulses. Both the transmitter which is generating a
given data word on a given data bus and all intended receivers of
the data, access that given data word simultaneously after each has
counted the same number of intervals from the synchronizing pulse
to the predetermined time slot.
Inventors: |
Heitlinger; Louis J. (Waukesha,
WI), Bahr; John P. (Wauwatosa, WI), Smith; John H.
(Milwaukee, WI), Anderson; Thomas W. (Greendale, WI) |
Assignee: |
General Electric Company
(Schenectady, NY)
|
Family
ID: |
23621758 |
Appl.
No.: |
05/409,738 |
Filed: |
October 25, 1973 |
Current U.S.
Class: |
340/870.09;
340/870.13 |
Current CPC
Class: |
A61B
5/00 (20130101); G08C 15/12 (20130101); Y02A
90/10 (20180101) |
Current International
Class: |
A61B
5/00 (20060101); G08C 15/00 (20060101); G08C
15/12 (20060101); H04J 003/00 (); H04J 006/00 ();
H04Q 011/04 (); H04Q 005/00 () |
Field of
Search: |
;340/172.5,150
;179/18FF,15AL,15 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Shaw; Gareth D.
Assistant Examiner: Sachs; Michael C.
Attorney, Agent or Firm: Hohenfeldt; Ralph G. Wiviott;
Fred
Claims
We claim:
1. A patient monitoring and data handling system for use with
hospitalized patients, comprising:
a. a plurality of data sending units for being placed in the
vicinity of a hospitalized patient and having means for producing
digital data words representative of information pertinent to a
patient and a plurality of data receiving units for being placed in
the vicinity of said patient and having means for receiving digital
words pertinent to monitoring a patient, each of said digital words
being assigned to a particular time slot in a sequence of time
slots,
b. first data bus means having a conductor for each bit in a data
word to permit parallel transmission of the bits comprising a
word,
c. means for connecting said sending and receiving units,
respectively, to said data bus, said last named means each
including gate means and gate enabling means associated with each
sending and receiving unit for selectively transmitting data words
between an associated sending unit and said data bus and between
said data bus and an associated receiving unit when gate means
associated with a sending unit and gate means associated with a
receiving unit are simultaneously enabled in time correspondence
with occurrence of a time slot to which the word to be transmitted
is assigned,
d. a source of constant rate clock pulses, said clock pulses
corresponding with said sequence of time slots,
e. means for generating a sync pulse signal in response to
occurrence of repeatable numbers of clock pulses,
f. pulse counting means associated with each sending and receiving
unit and each counting means responding to occurrence of each sync
pulse signal by simultaneously initiating counting of clock pulses
and continuing to count selected predetermined numbers of ensuing
clock pulses so that a counting means associated with at least one
of said receiving units reaches its predetermined number of counts
in coincidence with counting means associated with at least one
sending unit reaching its predetermined number of counts between
which units data assigned to a time slot corresponding with
occurrence of said coincidence may be exchanged,
g. the said gate means associated with the said ones of said
sending and receiving units, respectively, being enabled to respond
to said coincidence for said transmitting of said data words and
other of said gate means for words assigned to other time slots
being enabled sequentially in response to other coincidences at
predetermined times whereby respective sending units operate
synchronously with receiving units that are intended to receive
data from said sending units.
2. The system set forth in claim 1 including:
a. latch means for storing one of said digital word signals, said
latch means being coupled to one of said gate means.
3. The system set forth in claim 2 wherein:
a. at least one of said bedside station receiving units includes
oscilloscope display means for displaying said parameter in
correspondence with its original analog form, and
b. digital-to-analog conversion means associated with said display
means for converting parameter indicative digital words to
corresponding analog signal for driving said oscilloscope display
means.
4. The system set forth in claim 2 wherein:
a. at least one of said bedside station receiving units includes
oscilloscope display means for displaying said parameter in
alphanumeric form, and
b. means for converting said parameter representative digital word
signals to signals for driving said alphanumeric display means.
5. The system set forth in claim 1 characterized by:
a. a bedside station including at least one of said sending units
and at least one of said receiving units,
b. said bedside station sending unit comprising a functional unit
including input means for coupling to a patient parameter sensing
device to derive analog signals therefrom representative of a
patient parameter,
c. each of said functional units including analog signal
conditioning means, analog-to-digital word conversion means
responsive to said analog signals, digital word storage means and
interface means and means for coupling and uncoupling each of said
functional units to and from said data bus means independently of
any other units connected to said bus means.
6. The system set forth in claim 1 characterized by:
a. a bedside station including at least one of said sending units
comprising a keyboard means, said keyboard means being operative to
produce predetermined unique selectable system command digital
words for being transmitted by way of said data bus means to a
receiving unit for controlling said receiving unit.
7. The system set forth in claim 1 wherein:
a. said data bus means conductors have a single conductor for said
clock pulse and said sync pulse signals and a conductor for each
binary digit comprising a digital word.
8. The invention set forth in claim 1 including:
a. means associated with each sending unit for establishing a
parity bit for each digital word sent to said bus,
b. means at each receiving unit for checking the parity of each
received word, and
c. said data bus conductors including a single conductor for said
clock pulse and sync pulse signals, a conductor for parity bits and
a conductor for each binary digit comprising a word.
9. The system set forth in claim 1 wherein:
a. said data bus comprises no more than 10 conductors.
10. The system set forth in claim 8 wherein:
a. said data bus comprises no more than 10 conductors.
11. The system set forth in claim 2 including:
a. a central station for monitoring the condition of one or more
patients at said bedside station and for displaying and generating
data,
b. said central station including receiving unit means comprising
oscilloscope means for displaying data in alphanumeric form said
data corresponding with data represented by digital words from said
selected ones of said sending means,
c. said central station including receiving unit means comprising
oscilloscope means for displaying dynamic waveforms represented by
digital data words from sending units in the system and including
receiving unit means comprising means for converting digital data
from said sending means to a corresponding analog signal and strip
chart recorder means responsive to said last named analog signal by
producing hard copy of physiological waveforms represented by said
digital data words from sending units in the system,
d. central data bus means associated with said central station and
having a plurality of conductors,
e. a plurality of interface means respectively coupling said
receiving units to said data bus means at said central station,
and
f. means including interface means for coupling said central
station data bus means and said first data bus means.
12. The system set forth in claim 11 including:
a. sending unit means comprising keyboard means in said central
station, said keyboard means being operative to produce digital
data words representative of commands and data for use by selected
receiving units in said central station and said bedside station,
and
b. interface means coupling said keyboard means to said central
station data bus means.
13. The system set forth in claim 1 including:
a. a central station for monitoring the condition of one or more
remotely located patients and for displaying and generating
data,
b. at least one sending unit and at least one receiving unit in
said central station,
c. central station data bus means,
d. a plurality of interface means for coupling said units,
respectively, in said central station to said central station data
bus means, and
e. means for coupling said central station data bus means to said
first data bus means.
14. The system set forth in claim 13 wherein:
a. said bedside data bus means and said central station data bus
means have the same number of conductors.
15. The system set forth in claim 13 including:
a. a processing unit station remote from said central station and
said bedside station,
b. computer means at said processing unit station,
c. processing unit station data bus means,
d. interface means coupling said computer means to said processing
unit data bus means to permit bidirectional exchange of data words
between said computer means and said processing unit station data
bus means, and
e. means coupling said processing unit station data bus means to
said central station data bus means.
16. The invention set forth in claim 15 wherein:
a. said processing unit station data bus means and said central
station data bus means have the same number of conductors.
17. A system for handling data pertinent to at least one
hospitalized patient, said system being characterized by having at
least one bedside station to which said patient may be in proximity
and including one or more digital data sending units and one or
more digital data receiving units, said units being operative to
send and receive data respectively during existence of a time slot
assigned to said units from a sequence of time slots, said system
being characterized further by use of a data format wherein
discrete digital data words used in the system are assigned to said
time slots, respectively, said system further comprising:
a. means associated with said sending unit for producing digital
data words representative of information pertinent to said
patient,
b. data bus means associated with said bedside station, said bus
means having at least as many conductors as there are bits in the
data word having the largest number of bits of any word to be sent
in said system to permit parallel transmission of the bits
comprising a word,
c. said data sending units and said data receiving units being at
said bedside station,
d. means for controlling said sending units to transmit digital
data words to said data bus during the existence of the time slots
to which said words are respectively assigned and means for
controlling said receiving units to accept from said data bus only
those digital words in time slots corresponding with their
respective assigned time slots whereby to effect selective
transmission of words exclusively from a designated sending unit to
one or more receiving units,
e. a source of a clock pulse train and means for encoding sync
pulse information periodically in said pulse train,
f. means for coupling said sync pulse train to one of said data bus
conductors,
g. decoding means associated with each of said sending and
receiving units, respectively, said decoding means being settable,
respectively, to produce a control pulse corresponding in time with
a predetermined time slot, and
h. gate means coupling said sending and receiving units,
respectively, to said data bus, said gate means being responsive to
coincident control pulses at said sending and receiving units to
gate the word assigned to the determined time slot from said
sending unit to said data bus and from said bus to said one or more
receiving units within the same time slots.
18. The system set forth in claim 17 wherein:
a. at least one of said sending units at said bedside station
comprises:
1. a functional unit including input means,
2. physiological parameter sensing means adapted to be coupled to a
patient for producing an analog signal that is functionally related
to said parameter, said analog signal being coupled to said input
means,
3. analog-to-digital conversion means for converting samples of
said analog signal to corresponding digital words comprised of
binary signals, and
4. means for coupling said digital words to said gate means,
whereby response of said gate means to predetermined control
signals will place said words during their assigned time slots on
said data bus means.
19. The system set forth in claim 18 wherein:
a. at least one of said receiving units at said bedside station
comprises analog signal display means including oscilloscope means,
and
b. said receiving unit having means for converting digital word
signals taken from said bus during predetermined time slots to
signals for driving said oscilloscope means whereby to recompose
said analog signal.
20. The system set forth in claim 17 wherein:
a. at least one of said sending units at said bedside station
comprises:
1. means for receiving a waveform representative of a physiological
condition of a patient,
2. means for successively sampling the amplitude of said waveform
and means for converting waveform amplitudes to digital
representations thereof, and
3. said decoding means associated with said last named sending
means being set to operate corresponding gate means so as to couple
to said data bus means in rapid succession digital words
representations of the existing amplitude of said waveform.
21. The system set forth in claim 20 wherein:
a. said decoding means include means which are set to decode
consecutive blocks comprised of equal numbers of digital words, the
number of blocks times the number of words in a block constituting
the number of words in a train which corresponds with the number of
time slots, and
b. said decoding means producing a control signal for said gate
means for corresponding time slots in each block, said digitized
waveform samples occurring in each block at least once to thereby
provide for high resolution of said waveform.
22. The system set forth in claim 21 wherein:
a. there are 128 blocks in a work train and the clock pulse
frequency is such that said blocks are repeated at least 4 times
per second whereby to obtain waveform resolution of 512 samples per
second.
23. The system set forth in claim 20 wherein:
a. said decoding means includes means which are set to decode
consecutive blocks comprised of equal numbers of digital words, the
number of blocks times the number of words in a block constituting
the number of words in a train,
b. said decoding means producing a control signal for said gate
means for corresponding time slots in every fourth block, and
c. there being 128 blocks occurring 4 times per second whereby said
time slots for said digitized waveform samples occur at the same
medium resolution rate of 128 sampes per second.
24. The system set forth in claim 17 wherein:
a. said sync pulses occur 4 times per second and the clock pulse
frequency is such that 2,048 time slot defining pulse intervals
defining a train of an equal number of data words occur between
each of said sync pulses.
25. The system set forth in claim 17 wherein:
a. at least one of said sending units is adapted to send direct
line commands to a predetermined receiving unit in said system to
effect operation of said receiving unit,
b. means in said sending unit for producing selected digital words
constituting an encoded command signal, and
c. said command signals being assigned to time slots which are
repeated at equal intervals of time slots whereby to provide a
sustained train of the same command signals.
26. The system set forth in claim 17 wherein:
a. said train of time slots is divided into blocks of time slots
each of which is comprised of a predetermined equal number of time
slots for digital words, each block having a predetermined word
time slot for one or more system command words corresponding in
position with the time slot for those words in the next ensuing
block, and
b. said decoding means for said sending and receiving units,
respectively determining each time block and a producing said
control pulse upon occurrence of said command words, whereby a
particular command word may be presented one or more times in each
block so as to provide substantially continuous selected commands
from said sending unit to said receiving unit.
27. The system set forth in claim 17 wherein:
a. said data bus has no more than 10 conductors, 8 for said word
bits, 1 for said sync signal encoded clock pulses and 1 for parity
bits.
28. The system set forth in claim 17 including:
a. a central station remote from said bedside station, said central
station having at least one of said sending units and at least one
of said receiving units,
b. a central station data bus means,
c. means coupling said central station sending and receiving units
to said central station data bus, and
d. means coupling said central station data bus to said bedside
station data bus.
29. The system set forth in claim 28 wherein:
a. at least one of said central station receiving units comprises
data display means including oscilloscope means, and
b. means for converting selected ones of said digital data words
received by said unit to signals for controlling said oscilloscope
means.
30. The system set forth in claim 28 including:
a. a central processing unit station remote from said central
station,
b. said processing unit station including computer means for
storing data generated by said sending units and for generating new
data from said stored data such that said new data may be
transferred to at least one of said receiving units,
c. said processing unit station including data bus means, and
d. means for coupling said central station data bus means to said
processing unit station data bus means.
31. The system set forth in claim 28 wherein:
a. said bedside station data bus means and said central station
data bus means have an equal number of conductors.
32. The system set forth in claim 30 wherein:
a. all of said data bus means have an equal number of
conductors.
33. The system set forth in claim 30 wherein:
a. all of said sending and receiving unit means are connected in
parallel with their associated bus means to enable adding or
removing sending and receiving units without affecting data word
exchanges between pre-existing predetermined ones of said units or
units which remain, respectively.
34. The system set forth in claim 1 wherein at least one of said
means for producing digital words is constructed and arranged to
produce said words at one predetermined rate and at least another
of said means for producing digital words is constructed and
arranged to produce said words at another predetermined rate, said
rates depending on the demands of the system for the type of data
sent by said one and another means.
35. The system set forth in claim 1 including a plurality of
functional units at said bedside station in proximity with said
patient, at least one of said functional units including sensor
means adapted to be coupled with said patient to derive analog
signals representative of a physiological parameter of said
patient, means for converting said analog signals to parameter
representative digital words for being gated to said data bus.
36. The system set forth in claim 1 including means for producing
system command words for being gated to said bus to control said
system, said command words being assigned to individual time
slots.
37. The apparatus set forth in claim 36 wherein said commands
producible by said command word producing means include direct line
commands characterized by digital words comprised of selected ones
and zeros,
means coupled to said bus and subject, respectively, to being
commanded selectively to perform a function in correspondence with
a particular bit position in said word being a one or a zero, said
particular bits thereby constituting continuous bit streams
representing individual commands.
38. The apparatus set forth in claim 36 wherein said commands
producible by said command word producing means include digital
data words comprised of zero and one bits, said words being
assigned to particular time slots, said words respectively
comprising code bits corresponding with the type and destination of
the command and command bits corresponding with the command.
39. The apparatus set forth in claim 38 wherein at least some of
said command words, respectively, are selected from a class of
words corresponding with commanding setting of alarm limits,
changing data display formats, initiating test procedures and
controlling a strip chart recorder.
40. A system for monitoring hospitalized patients and for
transmitting data pertinent to said patient in and between a
bedside station and one or more stations remote from said bedside
station, comprising:
a. means at said bedside station for obtaining from a patient at
said station signals representative of information pertinent to
said patient,
b. means for converting said signals to data words in binary
digital form, each of said words being assigned to a particular
time slot in a sequence of time slots,
c. data bus means at said bedside station having a plurality of
conductors including at least one conductor for each bit in a data
word to permit parallel transmission of the bits comprising a
word,
d. at least one data sending unit and at least one data receiving
unit at said bedside station,
e. said sending unit including gate means selectively operable to
gate converted digital words produced by said converting means onto
said data bus at times corresponding with the time slots to which
the digital words are respectively assigned,
f. said receiving unit including gate means selectively operable to
gate digital words off of said data bus at times corresponding with
the time slots to which the digital words are respectively
assigned,
g. means associated with said receiving unit for utilizing digital
words gated from said bus,
h. a second station situated remotely from said bedside station and
having at least one data receiving unit,
i. second data bus means at said remote station and having a
plurality of conductors including at least one conductor for each
bit in a data word to be carried thereby to permit parallel
transmission of the bits comprising a word,
j. said remote receiving unit including gate means selectively
operable to gate digital words off of said second data bus at times
corresponding with the time slots to which the digital words are
respectively assigned,
k. means associated with said remote receiving unit for utilizing
digital words gated from said second data bus, and
l. means for coupling said bedside station data bus to said remote
second data bus.
41. The system set forth in claim 40 including:
a. a source of constant rate clock pulses, said clock pulses
corresponding, respectively, with said time slots in said
sequence,
b. means for generating a sync pulse in response to occurrence of a
repeatable number of clock pulses,
c. pulse counting means associated with each sending and receiving
unit, each counting means responding to occurrence of each sync
pulse by simultaneously initiating counting of clock pulses and
continuing to count selected predetermined numbers of ensuring
clock pulses so that a counting means associated with at least one
of said receiving units reaches its predetermined number of counts
in coincidence with counting means associated with at least one
sending unit reaching its predetermined number of counts between
which units digital data words corresponding with occurrence of
said coincidence may be exchanged,
d. said gate means associated with said sending and receiving
units, respectively, being enabled to respond to said coincidence
for gating said data words of a particular time slot and
prohibiting gating of words assigned to other time slots.
42. The system set forth in claim 40 including:
a. means at said second station for generating digital data words
which are assigned to a predetermined time slot,
b. a sending unit including gate means selectively operable to gate
digital words from said word generating means to said second data
bus at times corresponding with the time slot to which the words
from said generating means are assigned.
43. The system set forth in claim 42 including:
a. a source of constant rate clock pulses, said clock pulses
corresponding, respectively, with said time slots in said
sequence,
b. means for generating sync pulses in response to occurrence of a
repeatable number of clock pulses, and
c. counting means associated with said last named sending unit for
counting clock pulses from said source upon occurrence of a sync
pulse and responsive to counting a predetermined number of pulses
up to the one corresponding to the time slot of the word from said
sending unit by enabling said last named gate means for gating said
word to said second data bus means.
44. The system set forth in claim 40 including:
a. one or more additional bedside stations,
b. data bus means at each of said additional stations for
transmitting digital data words pertinent to said patient to and
from said station, each of said data bus means having a conductor
for each digit in said words, and
c. means for coupling said data bus means of each additional
station to said second data bus means at said remote station.
45. A system for generating and for utilizing data pertinent to a
hospitalized patient, comprising:
a. a bedside station and means at said station for producing binary
digital words representative of information pertinent to said
patient in said station, said words being assigned to a discrete
time slot,
b. a remote station,
c. means at said bedside station for utilizing digital words
pertinent to said patient and produced at said station or at a
remote station, said utilizing means using words assigned
respectively to a discrete time slot,
d. means at said remote station for producing binary digital data
words pertinent to said patient, said words being assigned
respectively to a discrete time slot,
e. means at said remote station for utilizing digital data words
pertinent to said patient, said words being assigned respectively
to a discrete time slot,
f. first data bus means at said bedside station and a second data
bus means at said remote station, each of said data bus means
having a plurality of conductors including one for each bit in said
digital words that are to be transmitted by said buses,
g. means for interconnecting said buses,
h. means for generating a repeatable train of clock pulses and
means for producing a sync pulse periodically in response to
occurrence of repeatable numbers of clock pulses, each of said
clock pulses corresponding with a discrete time slot,
i. means for coupling said sync pulse and clock pulse train to one
conductor in said data buses, respectively,
j. coupling means for coupling each of said digital word producing
means and each said digital word utilizing means to one and another
of said data bus means, each of said coupling means including gate
means for being enabled selectively to gate digital data words to
and from said data bus means,
k. pulse counting means for each coupling means, sid pulse counting
means each receiving said sync and clock pulses and each counting a
preset number of clock pulses up to the assigned time slot for a
digital word that is to be produced or used by said producing and
utilizing means, respectively, all counting means reaching the same
time slot coincidentally causing the gate means of word producing
and word utilizing means whose words are assigned to said time slot
to become enabled and other of said gate means for words assigned
to other time slots becoming enabled sequentially when other
coincidences occur.
Description
BACKGROUND OF THE INVENTION
This invention relates to a system for acquiring, processing,
storing, transmitting and displaying data relative to the
physiological condition of a critically ill patient in a
hospital.
The first generation of patient monitoring apparatus comprised
sensors attached to the patient to provide analog signals such as
the electrocardiogram (ECG), blood pressure, temperature, and
others. Detected analog signals were amplified and processed and
displayed essentially as analog signals on devices such as
oscilloscopes, calibrated meters and strip chart recorders.
Initially, this apparatus was located at the bedside of the
patient. In more advanced installations, a number of bedside units
were connected to a central station which had analog display
devices. This permitted medical personnel at the central station to
monitor the dynamic waveforms of several patients simultaneously
and to monitor perhaps one or two other physiological parameters
such as heart rate and respiration rate. Whenever a certain
monitored parameter from a certain patient exceeded a preset limit,
an audio alarm notified medical personnel of the problem. Thus, the
first generation of patient monitoring apparatus was primarily a
collection of analog units each performing a single function. In
addition, all data was transmitted in analog from between the
bedside and the central station.
The above-mentioned patient monitoring systems have several
disadvantages. Among them is that only the primary parameters such
as heart rate, systolic pressure, mean pressure and the like are
derived from the dynamic waveforms because of the limitations of
analog processing. Data could not be stored in the best form. Only
dynamic waveforms could be stored and reviewed later when some
alarm condition or anomaly occurred. Data transmission was limited.
A separate analog line was required for each waveform and each
derived parameter to be transmitted from any bedside to the central
station. Analog lines are susceptible to noise interference and
signal attenuation over a long distance. Any communication from the
central station to the bedside station required separate analog
lines from those used to transmit physiological data from the
bedside to the central station. Large amounts of physiological or
other data needed for optimum patient care required a number of
cables or an exceedingly large multi-conductor cable to
interconnect the bedside monitors with the central station.
Further disadvantages were inherent in data display. Each derived
parameter to be displayed simultaneously at the bedside or at the
central station required a separate meter or numeric display
device. When a number of physiological parameters and waveforms
were required for optimum patient care, the amount of display
hardware needed to monitor the patient became excessive,
distracting and more difficult for medical personnel to
monitor.
A further disadvantage in such prior systems as their lack of
expandability. Expansion of the number and type of waveforms and
derived parameters to be monitored at the bedside, once the initial
units were installed, required additional amplifiers, processors
and display devices or had to be modifications of the existing
display devices to share them. Taking either of these approaches to
expansion of the system was costly, inconvenient and difficult.
Expansion of the monitoring capability at the central station
usually required additional cables and additional display devices
to be installed which is again a task of major proportions.
A second generation of patient monitoring apparatus was designed to
overcome some of the disadvantages in data processing, storage and
display of the first generation of patient monitoring systems. The
second generation system added a central processor to the
previously existing bedside and central station units. The system
was thus endowed with a capability for deriving more complex
physiological parameters by way of computer programs, storing
derived parameters for later review by medical personnel, and
generating graphs and/or hard copy of stored data.
Among the disadvantages of the second generation patient monitoring
systems are that they had the same limitations on data transmission
between the bedside and central station units as the initial
systems. An additional set of analog lines were required to
transmit each distinct waveform and each distinct derived parameter
to the central processor. A separate set of digital lines were
required from the central processor to the digital display.
The problems relative to data display in the first systems were not
overcome in the second systems. In order to display parameters
derived in the central processor as well as the graphs of stored
data, display devices in addition to the analog devices already
present were required at the central station and possibly at each
bedside station to make the data accessible there. Moreover, the
limitations on the analog display devices of the first generation
systems were present in the second generation systems.
The second generation systems also lacked a capability for
convenient expansion. As in the first system, additional
amplifiers, processors, display devices and/or modifications of
existing display devices was required.
The second generation systems are not fully compatible with
computers or central processors. Since all of the data coming to
the computer is analog data, the system must first convert all of
the data to digital form before it can be processed or stored and
if the computer is used to drive an analog display device, the
computer output must be converted from digital to analog form
before it is able to control the display device.
SUMMARY OF THE INVENTION
The present invention constitutes a patient monitoring and a data
processing system which overcomes the disadvantages and limitations
in data transmissions, data display, system expandability and
computer compatability of the previously described prior systems
while at the same time retains the ability to process and store
data found in the second generation system. An important and
distinctive feature of this invention is the use of a set of
digital data buses and interfaces for two-way transmission of all
data between all units in the system. In general, in accordance
with the present invention, at the bedside of each patient there is
an assembly of subsystems which include sensors, signal
conditioners and hybrid processors, means for alphanumeric display,
means for dynamic display, a keyboard, and a set of digital
interfaces connected to a digital data bus at the bedside. This
bedside assembly acquires, processes and displays the current
values of up to 10 physiological parameters in numerical form in
addition to acquiring and displaying real time waveforms such as
blood pressure and ECG. Moreover, the bedside assembly can command
the central processor, if one is used in the system, to display at
the bedside computer derived parameters and the graphs of stored
parameter data.
Up to four bedside assemblies are interconnected with a central
station which is attended by one or more qualified medical
personnel. Interconnections to the central stations are
accomplished by way of a set of digital interfaces between the
bedside data buses and the central station data bus. The central
station comprises an assembly of subsystems which include a strip
chart recorder, an alphanumeric display, a dynamic display, a
keyboard and a set of digital interfaces connected to the central
stations digital data bus. The central station assembly displays
the derived parameters, dynamic waveforms, graphs of stored data
and the like for the patients at the four bedside stations served
by the central station. In addition, the strip chart recorder at
the central station provides hard copy of the ECG waveforms of a
specific patient whenever such copy is requested by the medical
personnel or automatically whenever alarm limits are exceeded on
one or more derived parameters from a patient.
The system may optionally include a central processing unit (CPU)
that features a small computer which receives parameter data,
keyboard commands from bedside or central station and selected
dynamic waveforms and provides as output more complex derived
parameters such as cardiac output, stroke volume and data
coordinate points for historical graphs. Medical notes, lab reports
and program variables and so forth may be entered into the computer
with a typewriter style keyboard terminal. This input and output
terminal also provides hard copy for any selected computer stored
or generated information.
Thus, the new patient monitoring and data processing system is
distinguished by its use of digital interfaces and digital data
buses arranged in a particular hierachy to intercommunicate
information between the bedside station, the central station and
the central processor as well as between individual subsystems
located at each site. The digital interfaces and digital data buses
allow addition or subtraction of subsystems at will since all of
the information is carried on the digital data buses as opposed to
having dedicated analog lines required for each distinct parameter
and waveform. The system is inherently computer compatible because
all of the data is communicated in digital format.
An important feature of the system is that the data buses use a low
number of conductors compared with the amount of information
communicated bidirectionally in the system. All data sources
convert information into digital words before transmission and all
receivers read digital words. The data sources or senders
throughout the system have binary counters which begin counting
simultaneously upon occurrence of a synchronizing (sync) pulse
which is applied to all of them at the same time so that they all
count in synchronism. Generated data words each have a time slot
which is identified by a count number with respect to a count
initiating sync pulse. The words are gated onto the data buses
synchronously and repetitively. The receivers have counters which
are all synchronized by the same sync pulse as are the senders so
they count correspondingly. Any receiver which is designated to
receive a particular word counts the same number as did the sender
when the data was gated onto the bus and the receiver is controlled
by a logic system as is the sender to open its gates simultaneously
to enter and store the data during its short appearance on the bus.
In an illustrative embodiment, the data words are presented in a
sequence of 16 words which constitute a block and 128 blocks which
constitute a train. Each word, thus, has its own time slot and a
time slot may be looked upon as a channel for particular
information. Because, in the illustrative embodiment, there are
2,048 words in a train and the train is repeated four times per
second, a large number of channels are open for conveying digital
information. Only about one-half of the 2,048 words have been
assigned, in a present commercial embodiment, to a specific piece
of data. Therefore, new data requirements such as additional
parameters or waveforms and the like can be accommodated easily in
the future by assigning them to some unused words on the bus and
expanding the system to include new data senders and receivers. No
additional data lines are required between the bedside and central
station or between central station and central processor.
Accordingly, a general object of this invention is to provide
apparatus for accurately and efficiently acquiring, deriving,
storing, communicating and displaying patient data.
A further object is to provide a patient data system which permits
practically unlimited addition, removal and interchange of
functional units so that the system can be expanded or modernized
to accommodate different and even yet undeveloped sensors, display
devices and other data producing and utilizing devices.
Another object is to transfer data on buses in digital form in
various selected modes by using synchronized multiplexing
techniques which avoid the need for sending address information to
intercommunicate any data sender or receiver.
Another important object is to reduce the number of conductors in
the data buses to a small number in view of the large amount of
data which is rapidly transferred and used in the system.
Another object is to have individual data buses associated
respectively with the bedside stations, the central stations and
the CPU stations and to have suitable interfaces between these
stations and their associated buses so that, in addition to the
system being adapted for easy expansion, it will also be fail soft.
Failing soft, as used herein, refers to the effect on the system
when any functional block or device fails in which case, in
accordance with the invention, the failed unit will not interact
adversely with the remainder of the system such that any other unit
would be made inoperative. For instance, a bedside station may
continue to operate even if there is failure of a unit at the
central processing station or the CPU station. In fact, a bedside
station could remain operative even though certain information is
not available to it due to failure of the CPU station. To further
exemplify the flexibility, a central station or CPU station may not
even be installed and yet the bedside station would be able to
acquire and display physiological data on the respective patients
in such stations. This fail soft mode contrasts with known digital
systems that have all of its units interconnected with a common bus
rather than individual buses.
Still another object of this invention is to improve patient safety
by enabling electrical isolation of a patient at a bedside station
from remotely located electric sources such as the central and CPU
stations. A corollary to this object is that the system is designed
for meeting electrical code requirements for avoiding
interconnecting patients in one room with electrical apparatus in
another room unless positive isolation can be provided which, in
the present case, is provided by the interfaces between all buses
and their associated units.
How the foregoing and other more specific objects of this invention
are achieved will be evidenced in the course of a description of a
preferred embodiment of the invention which will be set forth
hereinafter in reference to the drawings.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of the new patient monitoring and data
processing system;
FIG. 2 is a diagram of a clock and synchronizing pulse encoder used
in the system;
FIG. 3 is a diagram of a clock and synchronizing pulse decoder used
in the system;
FIG. 4 shows the waveforms incidental to operation of the decoder
in the preceding figure;
FIG. 5 shows the format in which information appears on the data
bus in accordance with one embodiment of the invention;
FIG. 6 shows some waveforms which are useful to explain how the
sequentially presented data words referred to in the preceding
figure are identified coincidentally by the sender and receiver of
the data;
FIG. 7 is for explaining the assignment of the bits in the various
data words in the illustrative embodiment of the invention;
FIG. 8 is a block diagram of a typical interface unit for receiving
digital data from a bus;
FIG. 9 is a block diagram of a typical data transmitter
interface;
FIG. 10 is a diagram of the logic elements for counting clock
pulses and decoding data words in accordance with their time
slots;
FIG. 11 is a diagram of a typical data latching arrangement;
and
FIG. 12 is a diagram of a typical driver for transferring data to a
bus.
DESCRIPTION OF A PREFERRED EMBODIMENT
FIG. 1 illustrates the general arrangement of the patient
monitoring and data handling system. The system comprises three
types of stations, a bedside station generally defined by a dashed
line block marked 10, a central station defined by a block marked
11 and a central processing unit station (CPU) marked 12. These
stations may be separated from each other by a considerable
distance in a hospital. There may be several bedside stations 10,
one in proximity with each patient who requires the close medical
surveillance which the system is intended to provide. Each bedside
station has the capability for deriving physiological information
about a patient, transmitting and receiving information to other
destinations and from other sources and for displaying information.
Various functions of the system may be controlled from the bedside
station 10 and from the central station 11 as will be
explained.
As indicated, one purpose of each bedside station is to derive
physiological data from the patient. Examples of such data are the
patient's heart rate, electrocardiograph (ECG), blood pressure,
temperature, partial pressure of both carbon dioxide and oxygen in
the patient's blood, blood pH and the like. Some of this data is
obtained in a form that allows it to be displayed directly at the
bedside station. Other data is processed in the CPU 12 and returned
to either or both the bedside station 10 or central station 11 for
display or other use. The CPU 12 has the capability for using
patient physiological parameter data to compute or derive
parameters in other forms which may be displayed at bedside or at
the central station. Typically there are up to four bedside
stations 10 for each central station 11. The CPU is an optional
feature. It may be disconnected or not installed but the system
will still have a good capability for measuring, communicating and
displaying data. A central station 11 may not be wanted in small
hospitals for economic or other reasons. The central station and
CPU can both be eliminated. One or more bedside units would, of
course, always be necessary. An important advantage of the system
is its flexibility which permits omission or additions of stations
or devices within stations. This is due largely to the use separate
data buses in the stations and to the manner in which data is
transmitted according to the invention.
Each bedside station 10 has a data bus 13 on which all information
is transferred to and from the station in digital form. Other
associated bedside stations would have buses such as 14, 15 and 16
which are shown fragmentarily to merely suggest their
existence.
The bedside station buses are interconnected with a common central
station bus 17 by means of suitable interface units 18-21 which
will be described in detail later. The central station has a
display unit 22 comprised essentially of a pair of oscilloscopes on
one of which alphanumeric (A-N) information concerning a patient
may be displayed on command of the attendant and on the other of
which certain waveforms such as ECG and blood pressure may be
displayed dynamically in realtime. The central station also has a
keyboard 23 of a specialized type by means of which the attendant
may issue system commands. The central station also has a central
auxiliary module (CAM) 24 which includes a chart recorder that may
be activated automatically or upon command to record current
physiological information. The CAM 24 also has visual and audible
alarms which are activated when certain of the physiological
parameters of the patient exceed preset limits. The various devices
22-24 in the central station are connected with bus 17 by suitable
interface units 26-29, as shown, to allow exchange of digital data
between the bus and devices.
Central station bus 17 is interconnected with a bus in CPU station
12 through a suitable interface 32. An interface unit 34 couples
the CPU 33 with bus 31. CPU station 12 has a central processing
unit 33 which is a small digital computer. The CPU receives
preprocessed data, provides more complex derived parameters, and
stores pertinent patient information. The computer receives derived
parameter data, keyboard commands and selected dynamic waveforms
and provides output data representative of more complex derived
parameters such as cardiac output, stroke volume and historical
graphs. The computer may store such medical data as fluid intake
and output together with patient treatment information when the
system is set to the medical data mode. In the CPU station there is
an input-output (I/O) device 35 for entering medical notes, patient
admission data, lab reports and program variables and the like. The
device 35 is coupled with bus 31 by means of an interface unit 36.
This device or terminal 35 also provides selected computer stored
or generated data in hard copy form. The CPU station 12 may also be
adapted to service other central stations similar to station 11 by
merely connecting its data bus 31 to the other central station with
a suitable interface such as the one marked 37 in FIG. 1. In the
system all interface-bus connections may be made with connectors or
cables having the same small number of conductors as the buses.
These connections are indicated with arrowhead lines in FIG. 1.
Before discussing in detail the manner in which data is
communicated and used in the system, additional general
characteristics of the bedside station 10 in FIG. 1 will be
examined. Each bedside station has a number of function blocks
typified by one marked 40. It will be understood that there may be
as many function blocks as there are unique types of physiological
parameter or other data to be handled. For instance, there would be
separate function blocks for ECG, blood pressure, body temperature,
blood gases such as CO.sub.2 and O.sub.2 and so forth. An important
feature of the invention is that these function blocks may be
easily plugged in and removed from the bedside data bus 13 so a
system may employ the function blocks for measuring physiological
parameters which are most appropriate to the type of care which the
particular patient needs. The plug-in feature facilitates expansion
of the system as patient numbers increase. It also permits adding
function blocks for parameters which may be of medical interest in
the future or for which the sensors have not as yet been
developed.
A typical function block 40 comprises a sensor 50 which derives
physiological information from a patient P and produces electric
signals for a waveform corresponding with a physiological
parameter. For instance, the sensor could be a blood pressure
transducer which converts pressure variations to a waveform signal.
Whatever form of signal is derived is usually amplified or
otherwise processed in what is denoted a signal conditioning module
51. For instance, an analog ECG signal is in the low millivolt
range and it is necessary to amplify it and filter it to eliminate
60 HZ interference or noise and to emphasize its fundamental
frequency of about 28 HZ before this analog signal is converted to
a digital signal. The required amplifier and filter circuits are
conventional and well known to those involved in the biomedical
electronics arts. The conditioned parameter signal is then
converted from its analog form to binary digital form in an
analog-to-digital (A/D) converter 52 as all information is sent and
received in digital form in the new patient data system. A
desirable A/D converter is the ramp type described in U.S. Pat. No.
3,051,939 dated Aug. 28, 1962. In a commercial embodiment a model
ZD 461 converter which is a successive approximation type, made by
Zeltex, Inc., 1000 Chalomar Road, Concord, Cal., was successfully
used. Further information on A/D conversion is obtainable from the
book "Computers in Biomedical Research", Academic Press, 1965, Vol.
2, Editors R. W. Stacy and B. D. Waxman, see particularly, Section
A-1, authored by Josiah Macy, Jr. The digital signals are then
stored in a register or other storage device which is marked 53.
The register may comprise two four-bit latches such as type 74175
which is available from several manufacturers. In this system
information is usually stored for a short interval at least at the
sending and receiving points since it cannot be put on the data
buses randomly but must be put on and taken off in the proper time
slot or in a synchronous mode. The synchronous mode of data
transmission used therein enables removal and addition of stations
and functional blocks without doing any rewiring as will be more
evident hereafter. Functional unit 40 is coupled with bedside data
bus 13 with an interface unit 54 which controls data transfer as
will be explained.
Data derived with the function blocks may be displayed in various
forms by means of a display unit 43 which is associated with each
bedside station. Display 43 is similar to display 22 in the central
station 11 and comprises suitable electronic circuitry for getting
data into the proper format and displaying it on a pair of bedside
oscilloscopes 44 and 45. The left oscilloscope 44 is used in one
embodiment for displaying alphanumeric data and alarm information
and the oscilloscope 45 is used for displaying some physiological
data along with waveforms representative of physiological
parameters. Display unit 43 is coupled to data bus 13 with suitable
interface units 47 and 48. Each bedside station also has a keyboard
46 for dictating commands to the system such as selecting certain
data for display and for communicating with the central station 11.
Keyboard 46 is coupled to bus 13 with an interface unit 49. The
keyboard 46 also has controls, not shown, for testing the various
physiological data processors of the system. For instance, when the
proper calibration switches are operated, the function blocks are
referred to standard built-in references and a predetermined number
for each derived parameter is displayed if the physiological
processor and its associated circuitry is properly calibrated.
In the new system all data is communicated in digital form using
buses 13 and 17 which use few conductors considering the amount of
information and the speed with which it is transferred. Bus 31 in
the CPU may have more conductors than 13 and 17. The buses are
interconnected with buses having a similar number of conductors
which are indicated by arrowhead lines in FIG. 1. Data
communication is in the synchronous mode so that no digital
addresses need be sent to transmit or receive data. Each data word
has its own unique time slot. Since the use of the customary
address information is avoided, the bit rate is lower and greater
immunity to noise is obtained. The availability of a large number
of unused time slots makes them available for system expansion.
Removal of any data generating or receiving unit merely clears some
time slots. Most data is on the data buses repeatedly so there is a
high degree of redundancy and single bit interferences or
transmission errors are of no consequence. The system is thus
unique in the way it permits subsystems to communicate with each
other.
The data communication features of the system will now be
considered. Functions of the data communication system are to
transmit system commands from the keyboards and CPU to all other
parts of the system, to transmit data from the function blocks to
the display format generators and CPU and from the CPU to the
format generators, to transmit system alarm messages from the
various system components to the displays and CPU and, to
synchronize the operation of the various subsystems.
A basic feature of the system is that data sending units place
digital data on the buses in a predetermined sequence and any
receiving unit that is supposed to receive particular data words or
bits is controlled to gate only the particular data in
simultaneously with its transmission. Thus, every data source or
sending unit is subject to the control of a clock pulse train. Each
sending and receiving unit has a counting device. A common
synchronizing pulse is generated and applied to all counters so
that they begin counting from time zero simultaneously. The
counters are associated with decode controls which enable gating
data from a particular sending unit onto the buses in preassigned
time slots for the various data words that are generated by the
sending units. The designated receivers for the data are similarly
provided with counters and decode controls which are synchronized
by making a corresponding number of counts to gate the data then
appearing on the bus into storage for realtime or subsequent use.
In one practical embodiment, the clock frequency is 65,536 Hz. The
sync code is phase modulated on the clock signal as a unique code
covering two clock periods. This code is repeated to produce one
sync pulse every 16,384 clock periods or every 250 milliseconds.
Each sync pulse is followed by a data word train of 2,048 digital
words or time slots for such words which are, of course, repeated
four times per second. Only an extremely large system would
actually use anywhere near this word capacity so generally there
are many time slots open and available for any additional devices
which a user may want to install to enlarge system capacity. Each
data transfer over the system data bus takes place at a
predetermined time established by counting a specific number of
clock periods following a system sync pulse. Since each data bus
interface receives the same sync code, and each interface is tied
to the same clock line, each interface will use the same amount of
time to count and will cause every receiver that is programmed to
receive data from the bus to turn on at almost exactly the same
time as the data is transmitted by the source unit. In this typical
system, data words may appear on the buses for 120 microseconds and
the programmed receivers have that much time to take the data
off.
The bus structures 13-17 and 31 are only 10 lines wide or, in other
words, comprise 10 conductors in one practical embodiment. There
are eight lines for the basic data format which is composed of
individual eight bit words or bytes and there is a ninth line for a
parity bit. The tenth line handles the clock pulses and the
periodically appearing sync pulse code. Each data entry is composed
of one or more words in straight binary, octal or binary coded
decimal form as required. The data structure and format and the
synchronous manner in which data is communicated will be described
in greater detail later. At present, a typical data sender and
receiver, called a function block 40 in the bedside station 10 of
FIG. 1 will be discussed to illustrate how typical data words are
composed, transmitted and received.
Typical function block 40 is comprised of a number of subblocks
which are marked with the numerals 50-53. The function block
includes a sensor 50 which is responsive to some physiological
parameter such as blood pressure, ECG, temperature or the like. A
variety of sensors are known to those skilled in the art so they
need not be elaborated. A sensor usually produces an analog voltage
or current that is functionally related to parameter variations.
The analog signals are usually processed in a signal conditioner 51
which may be simply an impedance matching amplifier. In accordance
with the invention, the analog signals are converted to digital
form in a substantially conventional analog-to-digital converter
52. The digital data is usually stored in a suitable memory which
may be a latch or register, symbolized by block 53, so this data
may be available for transfer to another place of use in the system
as required. The stored digital data may comprise a digital word
representing the parameter value derived from the sensor 50. The
data is transferred to bedside bus 13 through an interface unit 54
which puts data on the bus in the appropriate time slot. Interfaces
are also used to take digital data from a bus at the appropriate
time.
The interface 54 may include a parity bit generator and checker,
not shown in FIG. 1, to add a zero or a 1 to the binary word to
make the total of the digits an odd number. Functional units in the
receivers, of course, have a conventional parity bit checker which
determines whether an error has been made in data transmission by
determining whether the digits are still odd when they are
received.
The data words generated by a function block, such as block 40 in
FIG. 1, or generated by any of the data producing units such as the
keyboards 46 and 23 and the CPU 33, are gated to the various buses
in the proper time slot relative to system synchronizing pulses
from a master clock pulse and sync pulse generator 61 at the
central station but may be at any station to which may provide the
timing for the entire system including the components in bedside
station 10, central station 11, CPU station 12. Each bedside
station can also have its own clock and sync pulse generator, not
shown, so if the generator at the central station is disconnected
or fails, each bedside station will continue running on its own
clock without loss of the monitoring function at the patient's
bedside. This is another example of failing soft. Any interface and
its associated digital data utilization device is also controlled
by clock and sync pulses to gate data from the buses. As will be
explained, some of the interfaces are adapted to gate digital data
to and from the buses. In the present system, the synchronizing
pulses are encoded in the train of clock pulses and transmitted
throughout the system.
The clock and sync pulse generator will now be described in
connection with the schematic diagram thereof shown in FIG. 2 and
in reference to the waveforms shown in FIG. 4. This will be
followed by a description of the clock and sync pulse decoder which
is depicted in FIG. 3.
In FIG. 2, a crystal oscillator 70 is used to generate a stable
clock frequency which is divided down by two four-bit binary
counters 71 and 72 to produce a clock frequency which, in a
practical embodiment, was chosen to be 65,536 Hz. This clock
frequency appears on pin 9 of counter 72 and the line leading
therefrom is designated line A. The clock frequency waveform is
similarly designated line A in FIG. 4. This clock frequency is
divided down 14 more levels by a group of counters 75, 76 and 77.
The outputs of the counters 75-77 constitute inputs to a pair of
NAND gates 78 and 79. These gates have inverters 80 and 82,
respectively, connected in series with their outputs. The outputs
of the inverters are connected to a pair of input terminals of
another NAND gate 81. The third input terminal to NAND gate 81
connects to pin 11 of counter 72. The counting levels of counters
72 and 75-77 are so chosen that when their outputs attain logic 1
simultaneously, the inputs to NAND gate 81 are all at logic 1 and
the output thereof, line C, is logic 0. In this particular example,
this occurs every 250 milliseconds, or every 16,384 clock periods.
The phase relationship of the signal on line C relative to the
clock frequency in line A is shown in FIG. 4. The clock frequency
on line A is inverted by an inverter 83 whose output is designated
line B and its waveform is similarly designated in FIG. 4. The
outputs of inverters 83 and 84 connect to the dual inputs of NAND
gate 85. Line A and line C are respectively connected to the inputs
of another NAND gate 86. Line C acts as an enable line to gates 85
and 86 with only one gate being enabled at any one time. When line
C is logic 1, gate 86 is enabled, allowing line A to appear on line
D. When line C is logic 0, gate 85 is enabled, allowiing the
inverted line A (line B) to appear on line D, thus causing a phase
reversal everytime line C is at logic 0 which is during two clock
pulses each 250 milliseconds. The phase modulated signal is
similarly designated in FIG. 4. Line D constitutes the sync code.
The clock/sync signal that goes out on line D is distributed to all
data bus interfaces in the system where it is decoded by the
clock/sync decoder circuit shown in FIG. 3 which will now be
described.
The basic concept of the decoder circuit shown in FIG. 3 is to use
a phase-lock loop circuit to produce a stable phase reference
signal. This phase reference signal is compared to the phase
modulated clock/sync signal to decode the periodic sync code.
In FIG. 3, the phase modulated signal on line D is applied as one
input to an exclusive OR gate 90 which acts as a noninverting
buffer. Thus, the same line D signal appears on line 91 and 92 as
the output from gate 90. The signal on line 92, which is the same
as on line D, is applied to a phase-lock loop 93 through a filter
circuit 94 which is primarily a voltage divider to bring the
voltage on line 92 from 5 volts to 1 volt in this design. The
circuit 95 includes a potentiometer and a series connected resistor
which set the free running frequency of the phase lock 93 in
conjunction with the capacitor 96. The two capacitors 105 and 106
in circuit 95 have to do with stability and the capture range of
the phase lock. Its phase comparison circuit requires a reference
signal that is 90.degree. out of phase with its input signal in
order to give a stable output. The output from the phase-lock loop
is coupled to a phase shifter 97 through a transistor 98 and an
exclusive OR gate which acts as an inverter. Integrated circuit
phase shifter 97 is a type 7474 flip-flop. Pins 12 and 5 of phase
shifter 97 are connected with phase-lock loop 93 by means of line E
on which the reference signal is 90.degree. out of phase with the
clock/sync phase. This is used to control the phase-lock loop
circuit. The line E signal waveform and its phase relationship is
illustrated in FIG. 4. Phase shifter 97 produces another output
which is the clock frequency appearing on line F and has the phase
relationship illustrated by its waveform in FIG. 4. The signal on
line F, which is in phase with the clock/sync line, is used to
demodulate the sync signal.
Adequate information on phase-locked loops (PLL) is obtainable from
the book "Analog Integrated Circuit Design" by A. B. Grebene, Van
Nostrand Rheinhold Co., 1972, Library of Congress Catalog Card No.
72-3869, pages 298-326. See particularly page 307, FIG. 9.20 and
description thereof. For PLL 93 in FIG. 3 hereof, a Signetics model
NE 565 was used. As indicated above the phase shifter 97 used in
the PLL is a flip-flop type 7474 which serves as the divide by N
counter, where N = 2, which is required by the FIG. 9.20 circuit.
Further information on PLL's is obtainable from the basic book
"Phase Lock Techniques", by F. M. Gardner, Wiley, New York,
1966.
Demodulation of the sync code is done by the integrated circuit
exclusive OR gate 99. It gives a high level output whenever line D
and line F are out of phase. Its output appears on line G which is
an input to an integrated circuit shift register 100 which is a
type 74195 in an actual embodiment. The outputs of register 100
appear on lines H, I, J and K, and their waveforms and phase
relationships are similarly designated in FIG. 4. Lines H-K are
connected as inputs to NAND gate 101. When all four of the shift
register output lines are at a high level, NAND gate 101 will
generate a sync pulse which appears on line L, and has the waveform
and phase relationship with respect to the clock signal on line F
that is illustrated in FIG. 4. The clock and sync pulse waveforms
are transmitted concurrently on one of the conductors set aside for
that purpose in each of the buses. Thus, the encoded signal
produced by the clock pulse and sync code generator of FIG. 2 is
transmitted throughout the system by means of the buses and this
signal is decoded at the point of utilization by a suitable
interface using the clock/sync decoder of FIG. 3. As explained
earlier, in one commercial embodiment, the sync code is repeated to
produce a sync pulse every 16,384 clock periods or every 250
milliseconds. Thus, there are four sync pulses per second. Each
sync pulse is followed by a data word train of 2,048 digital words
which train is repeated four times per second or each 250
milliseconds. A digital word may have as many bits as there are
conductors for carrying such bits simultaneously in the buses. In
the present case, there are eight such bit lines in the buses and,
as mentioned earlier, there are ninth and tenth lines for the
parity bits and clock/sync pulse waveforms, respectively. In the
illustrated embodiment, data words from the various sending devices
are put on the buses in a predetermined repetitive sequence. Any
identified data word will always be in the same time slot relative
to the sync pulse. The words are transmitted in sequential blocks
of which there are 128 in one embodiment. This facilitates
decoding. Each block contains 16 digital words. The manner in which
the interfaces decode the words and blocks for sending or receiving
by their associated devices will now be explained.
The clock/sync decoder just described in reference to FIG. 3 is
used in each interface associated with devices that receive, send
or both receive and send digital data. A typical receiver interface
is shown in block form in FIG. 8. This interface may be one like
interface 47 in FIG. 1 associated with dynamic display 45. A
clock/sync decoder such as is shown in detail in FIG. 3 is shown in
block form in FIG. 8 and marked 110. The encoded clock signal comes
in on line 111 in FIG. 8 which is fed from line D, the output of
the clock/sync generator in FIG. 2. The output from clock/sync
decoder 110 consists of the continuous train of clock pulses which
appear on line 113. The separated sync pulse appears on line 112.
These clock and sync pulses are fed to a binary counter array which
is designated generally by the reference numeral 114. The binary
counters in this and all other interfaces are triggered to start
counting clock pulses when they receive the sync pulse which occurs
simultaneously throughout the system. A word and block timing
decoder is used to count the individual digital data words
corresponding with the counts produced by the binary counters and
to also count the blocks. When the decoder determines that a
particular data word has occurred in a particular block which it
has counted, the decoder 115 produces an output pulse. Incoming
digital data words consisting in this case of eight binary digits
constituting the word and a parity bit come in on a 10 conductor
data bus 116. As mentioned earlier, the encoded clock signal comes
in on conductor 111 which is the tenth conductor of the data
bus.
Each receiver interface such as in FIG. 8 has an input buffer and
latches which are indicated in block form by the numeral 117.
Digital words on the data bus are gated into the input buffers and
latches when the timing decoder produces a strobe pulse coincident
with existence on the data lines of a particular data word which is
supposed to be accepted by the specific interface. By way of
example, data words can be transferred from the data buses to the
latches in about 120 microseconds. Of course, the block 117 in FIG.
8 which is indicated as being an input buffer and latch also has
means for making a parity bit check. If parity is wrong, the strobe
pulse from the decoder 115 will not enable the latches 117 to
accept the data from the data bus. A transmission error in a data
word will usually not affect the receiving device adversely.
Depending upon the category of the data word, the same word could
reappear in less than two milliseconds in the case of words from
the CPU or never reappear if they are transitory waveform values or
physiological parameter words but in the last two cases the last
correct data remains in the latch until the new correct data
arrives. In the case of system commands, which are a constant train
of words, the operator would initiate the command so a data word
drop-out is immaterial.
In FIG. 8, a dashed line rectangle 118 defines a block which is
identified as storage processing and converter devices. Such
devices for storing digital data words or bits and converting it to
analog form or using it to perform a particular function are known
to those skilled in the art and need not be described in detail.
The data, in whatever form it is processed, may be used to drive a
display such as the one defined by the dashed block 119 in FIG. 8.
The alphanumeric display 44 in FIG. 1 is typical of devices that
can be driven with digital information transmitted from a remote
source over data bus 116.
A typical transmitter interface such as interface 54 associated
with functional block 40 in FIG. 1 is depicted in block form in
FIG. 9 which will now be briefly described. This type of interface
also uses a clock/sync decoder 125 which receives the encoded
clock/sync signal from a data bus conductor 123. The decoder
separates the sync pulse from the clock pulses and uses the sync
pulses appearing on line 126 to start the binary counters 127
counting the clock pulses which are delivered from the decoder by
way of a line 124. A word and block timing decoder 128 counts the
clock pulses and produces an output signal at a time corresponding
with the time at which the particular data words from the
particular transmitter are to be placed on the transmission bus
129. In other words, when the decoder produces a strobe pulse it
enables a data bus driver 130 to transfer the digital data that is
available to data bus 129 in the appropriate time slot. In FIG. 9,
the data may be derived from any functional unit such as a unit 40
in FIG. 1. As in the case of the previous figure, data is derived
from a patient 131 by a physiological parameter sensor 132. The
sensor signals are usually in analog form and, as explained
previously, they are conditioned and converted to digital form in a
suitable device 133 and the digital data words so produced are made
available to the data bus drivers 130 for being transferred to data
bus 129 in the appropriate time slot.
The system also uses interfaces which are adapted for both
transmitting and receiving data to and from the buses. Such
transceiver interfaces need not be described in detail since they
can be readily devised by those skilled in the art in the light of
the foregoing description of the individual transmitter and
receiver interfaces.
A typical combination of binary counters and a word and block
timing decoder is shown in FIG. 10. This combination corresponds
with counters 114 and decoder 115 in FIG. 8 and with counter 127
and decoder 128 in FIG. 9. As explained in general terms
heretofore, the word and block decoder takes in the various count
stages of the binary counters and produces the time intervals at
which the associated device is to transmit or receive data. In this
particular embodiment, there are 2,048 time intervals in an array
of 128 blocks, each of which has 16 digital words in prescribed
time slots.
In FIG. 10, four divide by N counters are marked 140-143. Pin 14 of
counter 140 receives the clock pulses from which the sync pulse has
been separated. The counters are all reset to zero or enabled to
count when they receive on their pins 2 and 3 a sync pulse on line
144. Certain outputs from counter 140 are designated T0 to T3.
These connect to a NAND gate 145. T2 has an inverter 146 in series
with it. The output of NAND gate 145 produces a pulse in the middle
of a time slot that is allotted for one data word. In other words,
NAND gate 145 produces an output strobe pulse in the middle of the
interval when the W0 pulse is low and it produces another strobe
pulse in the middle of the next interval when the W0 pulse is high.
W0 is the basic frequency which determines the number of words in
the train. One-half of a W0 period comprises one data word. The
strobe pulse is inputted to a NOR gate 147 whose output is the time
strobe pulse as indicated by the legend in FIG. 10. The reason for
wanting a strobe pulse is that the latches are edge triggered and
it is desirable to enter data words in the latches at the middle of
the time interval during which the word exists on the data buses.
This assures that the words will be transferred to or from the data
buses without overlapping the next time slot.
Counters 140 and 141 in FIG. 10 have outputs marked W0-W3. These
are connected to the inputs of a NOR gate 149. W0-W3 make up the 16
data words. NOR gate 149 monitors counters 140 and 141 to determine
the position of the word in a block of 16 consecutive data words.
Switching any two input lines W0-W3 to NOR gate 149 will cause its
output to switch at a different time so that a different word in a
different time slot is selected in the particular block.
Counters 141, 142 and 143 have output terminals marked A0-A6. One
group of these outputs is connected to the input terminals of a NOR
gate 150 and another group is connected to a NOR gate 151. NOR
gates 150 and 151 select the block in which the data word of
interest appears. As mentioned, in the present system there are 128
16-word blocks and this makes up 2,048 words in a train. The input
connections to NOR gates 150 and 151 can be interchanged for
selecting different blocks. The combination of outputs from NOR
gates 149-151 is inputted to a NAND gate 152. The output of this
NAND gate occurs when the right combination of word time and block
time exist. In this way the time for transmitting or receiving a
specified word in this time slot can be determined. The output from
NAND gate 152 is fed to an inverter 153 whose output constitutes
the word time enable pulse for enabling the gates which transmit
data in respect to a data bus. A transmitter decoder uses all the
gates shown in FIG. 10 except 145-147. A receiver would duplicate
all of the other devices and would include 145-147. The output of
gate 147 would operate the latches for receiving the data word.
FIG. 11 shows the latches in block form which are used in the
various interfaces for holding a data word for utilization after it
is removed from the bus or for transmission to a bus in the proper
time slot for the designated word. In FIG. 11 there are two
four-bit latches 160 and 161. The incoming digital word bits from
the data bus are on a number of lines corresponding with a number
of data bus conductors and are marked B0-B7. In addition to these
eight data bits, there is an incoming parity bit from the ninth
line of the data bus. All of the incoming lines have an inverter
such as the one marked 162. A parity bit checker 163 is used to
determine if the incoming data word has an odd or even number of
bits. Since odd parity is used in this example, an even number of
bits in a digital word would indicate error and the word would be
prohibited from entering the latches. An eight conductor cable 164
has one conductor connected to each of the bit lines and to the
parity checker. Accepted binary words are outputted from the
latches on lines marked b0-b7, correspondingly with the input
lines. The latches are enabled for accepting a word by a gate 165.
The gate has the parity checker output and the strobe and enable
pulses from the decoder as inputs. When the strobe occurs and the
gate is enabled by the decoder, if parity is correct, the gate
strobes the latches or enables the latches to accept the data from
the bus.
FIG. 12 shows a block diagram of a typical data bus driver. This
device is used to transfer generated data from its source to a data
bus. The driver comprises nine NAND gates 170-178. Generated data
bits appear on the corresponding input terminals b0-b7. These bits
cannot get through the gates to outputs B0-B7 until the gates are
enabled. An enable pulse from a timing decoder, marked 179 in FIG.
12, is applied to one set of corresponding inputs of the NAND gates
170-178 when the data word is to be gated in its proper time slot.
The data bus driver assembly also has a parity bit generator 180
which has a multiple conductor cable 181 leading from it. One of
the conductors connects to the respective input terminals of the
various gates. In this manner, the parity generator determines
whether the data word handled by NAND gates for bits B0-B7 has an
odd or even number of bits. If the number is odd, the parity
generator enables parity bit gate 178 so it produces a bit which in
combination with the output bits B0-B7 is odd. In this module, when
any incoming bit is present and one input terminal of a NAND gate
170-178 is high, the output of that NAND gate will be low which
means that data bits are transmitted by effectively grounding the
line in the data bus for that bit.
It should be appreciated that interfaces such as 48, 49 and 54
which interface functional units in a bedside station such as a
typical station 10 with bedside data bus 13 are all the same basic
type of interface. Interfaces 26-29 which interface functional
units in the central station 11 with central station bus 17 are
also the same and the same as interfaces 48, 49 and 54. Each of
these interfaces have a clock and sync pulse decoder such as that
shown in FIG. 3 for yielding separated clock and sync pulses. They
also have data block and word decoders such as the one described
and depicted in connection with FIG. 10 for yielding time strobe
and word time enable pulses at a time which corresponds with a time
slot or the transfer time of a digital word which the particular
decoder is set to institute. The word and block timing decoder 115
in a typical receiver interface is shown related to the other
components thereof in FIG. 8. It will be understood that binary
counters 114 in FIG. 8 are collectively the same as counters
140-143 in decoder of FIG. 10.
The typical transmitter interface shown in FIG. 9 also has a
clock/sync decoder 125 such as is shown in detail in FIG. 3.
Moreover, this interface in FIG. 9 has the binary counter block 127
which represents the group of counters 140-143 in FIG. 10 and the
word and block timing decoder 128 which represents the other logic
circuit elements and circuitry of FIG. 10.
The strobe input buffer and latch block 117 in the receiver
interface in FIG. 8 is constituted by the components of FIG. 11
where inverters 162 are the input buffers. Type 7404 inverters were
used but there are other commercially available types that may be
substituted. The latch in block 117 of FIG. 8 is the equivalent of
the pair of four-bit latches 160 and 161 in FIG. 11. Two latches
were used to permit handling eight-bit data words. Type 74175
latches were used and this type may be used for any latch in the
system. Essentially, the latches are parallel access shift
registers which permit applying an input to each stage
simultaneously. The latches store one data word, comprised of up to
eight bits at a time.
The transmitter part of the interfaces also include the data bus
drivers shown in FIG. 12 and discussed in detail elsewhere herein.
The receiver part of the interfaces include parity bit checkers
such as 163 in FIG. 11 and the transmitter uses parity bit
generators such as 180 in FIG. 12. The parity bit devices used were
type 74180. Those skilled in the art know or can readily obtain
information on parity bit error checking as used herein from the
book "Logic Design of Digital Systems", D. L. Dietmeyer, 1971,
published by Allyn and Bacon, Library of Congress No. 72-134847,
particularly chapter 1.9, page 49 et. seq., and bibliography cited
therein. Further information is obtainable from the classic "Error
Detecting and Error Correcting Codes", R. W. Hamming, Bell System
Technical Journal, Vol. 29, No. 2, April 1950, pages 147-160.
Interfaces 18-21 between respective bedside data buses 13-16 and
central station data bus 17 could each comprise a set of
bidirectional synchronously operated switches, one for each data
bit plus one for the parity bits and the sync pulse encoded clock
pulses. Thus, the set of switches in interface 18 could be closed
when it is desired to transfer data from bedside bus 13 to central
station bus 17 or vice versa. The other interfaces 19, 20 and 21
may be closed in sequence to transfer data between bedside station
buses 14, 15 and 16 and central station bus 17. However, since
there may be considerable distance between a central station bus 17
and the individual bedside buses 13-16 it is preferable to amplify
the individual bit currents to overcome drop caused by line
impedance and to improve the signal to noise ratio. The interfaces
between buses also provide for isolation against high voltage which
might be accidentally applied to devices in the system.
Although the components are not shown, an interface for between
buses may comprise a driver and receiver combination at each end
having their outputs and inputs, respectively, connected to the
primary windings of isolating pulse transformers. There is one such
arrangement for each data bit and for the clock/sync pulses. The
transformer secondaries are connected by the long lines between
remote buses. When the driver at one bus is enabled by a
synchronizing clock pulse the receiver at the other bus is enabled
simultaneously. The system may also operate conversely so data can
be transmitted in either direction. Digital signal isolation
techniques are discussed in the magazine "Instrumentation
Technology" July 1973, pages 60 et seq.
Interfaces 32 and 37 which interface central station bus 17 with
CPU station bus 31, except for their timing are essentially the
same as interfaces 18-21.
The buses in this system carry five different categories of
information. The first category is system commands. These commands
can originate in three different locations: the bedside keyboard
46, the central keyboards 23 or the CPU. These commands may set new
alarm limits, change the display format, initiate test or
calibration procedures and control peripheral equipment for
example. The basic system command consists of an eight bit command
word plus a parity bit. Each command consists of special code bits
that indicate its destination and type. The code bits are used by
the system components to identify those commands addressed to them.
In an eight bit command word, the four least significant bits may
constitute the command, the next two most significant bits may
indicate the type of command; that is, whether it is sequential for
general control, or numeric. The two most significant bits are used
to indicate the destination; that is, whether the command is to go
to the bedside display, central station, computer or elsewhere in
the system. In the data bus format shown in FIG. 5 which will be
discussed in detail later, the system command words are designated
by the letters KA to KD. The system commands have the purpose of
getting a subsystem to respond to the operator, for example, to
turn on a strip chart recorder at the central station 11 from the
bedside station 10 or to get information from the CPU 33. System
commands are generated only once.
Within the category of commands is another type called the direct
line command (DLC) for convenience. Whereas the system commands are
usually expressed in terms of a three digit octal code word, the
direct line commands are generally expressed by changing single
bits in a word. DLC commands are continuously generated until
canceled by the operator. Use is typified by making a system test
by depressing the suitable test button, not shown, on one of the
keyboards 23, 46 which commands setting the function blocks such as
40 to produce stored test data for calibration purposes. Each bit
in this command category is sent at a fixed repetition rate as a
continuous bit stream for as long as the input device is activated.
The receiving unit converts the bit stream into a sustained logic
level that is held as long as the bit stream continues. Direct line
words are designated in the data bus format of FIG. 5 by the
letters DL followed by a pair of further letters indicating the
individuality of the command. The term direct line is employed to
signify that the continuous bit train imposed on the bus has the
operative effect of a wire directly connecting the sending unit and
receiving unit of the command.
Another category of information includes the measured physiological
parameter values. A purpose of the system is to measure and derive
parameter values and display them for medical use. The data
communication carries these parameters represented by digital
words, from where they are derived to where they are used or
displayed. It also carries indicators for system alarms, trend
values and trend alarms. Data indicating the trend of a parameter
is stored in the CPU and associated information is so extensive
that most parameters must be expressed in three consecutive words
as indicated by the consecutive designations PA0, PB0 and PC0 in
the 16 word set or block zero (BK0) in FIG. 5. The next in the
series of 128 available parameter slots in block BK1 is designated
PA1, PB1 and PC1 and so on through the blocks 0-127. One may see
that these parameter values are each repeated four times per second
since the entire train of data constituting 2,048 words is repeated
four times per second. PA and PB come from a function block and PC
comes from the CPU.
Referring to FIG. 7 where the bit assignment for the data structure
is shown, the interpretation is: P0-P9 is a binary number giving
absolute parameter value; PB has a sign bit 0 if positive and 1 if
negative; T0-T5 is a binary number giving the computed trend value
from the CPU; PC is a sign bit of the trend value, 0 if positive
and 1 if negative; the trend limit alarm is a CPU generated flag
bit, 1 if a trend alarm condition exists; parameter select relates
to display control bits, 1 if the parameter has been selected; and,
four individual system alarms, B6 and B7 in both PA and PB.
The parameter value, system alarm code and parameter select bit are
generated in a function block. The trend value and trend alarm bit
are generated by the CPU. Each data format location within the
parameter channel is preassigned by the system structure to a
specific parameter. If the function block designated to generate a
given parameter is not in the system, PA and PB for that parameter
number will be unused. If there is no CPU in the system, PC will
not be used. There cannot be a PC, of course, if there is not a PA
and PB for a given parameter.
Another category of information transmitted by the buses is
computer generated data. This data is designated by CA, CB, CC and
CD in each block of words as is evident in FIG. 5. The computer
data category involves transmission of display format data from the
CPU to one of the displays. For instance, it may be desired to
command the computer to display a graphical plot of a derived
parameter. Recall that a display usually shows a current value of a
physiological parameter, but the computer stores this information
and will later send out digital data providing the proper row and
column location of points to compose a graphical display. Thus, the
display formats used by the computer are unstructured, allowing it
to determine the specific row and column location for each
character it sends to the display. Each data transmission consists
of a 36 bit data field composed of 9 bit words including parity.
The bit assignment in the words may be seen in FIG. 7. Row CA
provides the address of the character location in the display
format. The row information digits R0-R4 in FIG. 7 compose the
first word CA in each of the blocks 0-127 in FIG. 5. CB designates
the column address of the character location in the display format.
CB consists of 6 bits as can be seen in FIG. 7 and is the second
word in each of the blocks in FIG. 5. The type of character code,
that is, whether it is ASCII code or graphical code is designated
by CC in the bit assignment and one may see in FIG. 7 that 6 bits
are used to provide this information to the display. Supplemental
information on character size, type and other information as can be
seen in the bit assignment chart of FIG. 7 are designated by CD
which appears as the tenth word in each block in FIG. 5. Note that
individual bits B0-B4 comprise these computer data words but that
the bits in each word are given a specific assignment. In other
words, individual bits convey the operating information rather than
the word itself.
The fifth category of information used in the system includes flag
words which are used to provide a fast response to a condition that
occurs somewhere in the system. The flag words are designated FA
and FB. By referring to FIG. 5, one may see that FA repeats at the
rate of 512 times per second and FB at 1024 per second. The flag
bit words have 8 bits but there is no association between the bits.
Each bit represents special information. For example, every time an
R-wave is recognized as being present in the ECG, a flag word bit
is set. The computer uses this information for some other activity.
Specific flag bit assignments are as follows: a high limit alarm
bit indicates an alarm condition for the parameter immediately
preceding this flag; low limit alarm indicates the same for the
parameter immediately preceding this flag; blank page confirm
indicates the computer data transmission sent in the preceding
computer data category CA, CB, CC and CD was correctly received by
the display; WA and WB indicate when the following waveform channel
is being used to send active data; SUS indicates or flags a
systolic upslope from an arterial pressure function block; and the
R-wave flag indicates the ECG function block has detected an
R-wave.
What might be considered another category of information is that
which expresses the digitization of waveforms for transmission to
the various displays and to the computer. There are means for
providing high resolution waveform samples WA and medium resolution
waveform samples WB. WA has two channels, WA0 and WA1, each
providing 512 eight bits, with parity, dynamic waveform samples per
second. This provides a frequency response in excess of 100 Hz.
The medium resolution dynamic waveform samples WB0-WB7 each provide
128 bits per second, with parity. This permits a frequency response
in excess of 25 Hz.
One may see in the FIG. 5 data bus format that high resolution
waveform words WA0 and WA1 appear in each block and since there are
128 blocks occurring four times per second there are a total of 512
waveform samples per second. FIG. 5 also shows how WB0-WB7 appear
in every fourth block so for these there are 128 samples per
second.
Conversion of analog waveform values to digital is a process well
known to those skilled in the art so that it will not be elaborated
nor will the equipment for performing this process be discussed.
Suffice it to say that the analog-to-digital converters receiving
the dynamic waveforms in the function blocks are running in
reference to an independent clock so the intervals between samples
are fixed and uniform. The information put on the buses is simply
representative of the waveform amplitude at each clock pulse cycle.
At a bedside station, for instance, a function unit derives analog
waveform information and converts it to digital information. At the
receiving end, such as at the display 43 in FIG. 1, the digital
information is reconverted to analog form. To avoid steps in the
waveform when it is recomposed for display, the original wave must
be sampled at a frequency that is higher than the highest frequency
component in the waveform. Usually it is desirable to sample at a
rate of 4 to 5 times the highest frequency. Thus, in the present
system where the ECG wave highest frequency component is around 40
Hz, a sampling rate of 256 per second could be used but a rate of
512 per second is actually used to permit accommodating future
devices whose waveforms have a fundamental frequency of 100 Hz or a
little more.
To recompose a smooth analog curve from digital data one must be
concerned with the increment between two successive digital values
or samples. Where each analog sample is converted and expressed in
eight binary bits a resolution of 256 bits is obtainable with
unique codes which set unique amplitudes. Thus, good vertical
resolution is easily obtainable.
Now that the data word sequence presented substantially
repetitively and synchronously on the bus system has been described
in reference to FIG. 5, the timing functions of the counters and
decoders in the interfaces will be re-examined in reference to FIG.
6. Also reconsider FIG. 10. In connection with FIG. 10 there was an
explanation of how the NOR gates 149-151 cooperated with the
counters 141-143 to produce an enabling pulse for gating digital
data to or from a bus, for instance. Also mentioned was the fact
that gates 149-151 could have their inputs variously connected to
produce an enabling pulse for transferring each word in the series
of words in FIG. 5 in its proper time slot.
In FIG. 6 the 16 data word time slots have the column numbers 0-15.
The first row is marked C0 and its frequency is 1/16 of the clock
frequency. The waveform C0 appears repetitively on one counter
output and the waveforms C1-C3 appear as shown in FIG. 6 on the
other W or word count terminals of the counters. Thus, if with a
first combination of W inputs to gate 149 it will see the waveform
condition in column zero, which is a coincidence of four binary
zeroes which is the code for word 0. If the inputs to gate 149 were
differently connected they would produce an output enable pulse
when the column 1 time relationship existed which is binary 1000.
Similarly for column 2 which would be a connection of the gate 149
to produce a word enable pulse for binary 0100 and so forth for the
other words in the series of 16 in each block.
The blocks in which the words exist are similarly determined: In
FIG. 6 the waveforms for the block determination are designated B0
to B127 for the 128 blocks. The seven inputs A0 to A6 of NOR gates
150 and 151 can be variously connected to produce an output pulse
for combining with the word pulses to select the proper word in
accordance with the block it is in. Here, block B0 would be
designated by binary 0000000 and block B127, the 128th block would
be designated by binary 1111111. In this manner the interfaces can
select any data word or words to which it is set.
Although numerical values have been used throughout this
specification for the sake of explaining the principles of the new
patient data system in relation to concrete rather than abstract
examples and although a specific embodiment of the system has been
described in detail, it will be understood that such description is
intended to be illustrative rather than limiting, for the invention
may be variously embodied and is to be limited only by construction
of the claims which follow.
* * * * *